1990 AC problems from Ottawa Canada

AC stopped working after EGR valve replaced

My son a ford mechanic spent 4 hours and came up with the following

All fuses OK, Previously when grounded the AC Relay in dash AC worked

Now seems to be an issue with low pressure cut off switch. Have to bypass now to make AC work when jumping relay.

Wire coming from heater/AC programmer to ECM - cut wire and 5v when AC on 2.5v when off (selected from head unit)On the ECM side 13.65 v all the time

Reconnect wire 13-10 v -  not really charging when A/C selector pressed on head unit.  Is it a pinched wire? Near intake manifold? He got frustrated - ECM not grounding AC relay because of this 13 v

Any help, tips would be appreciated.